15. Why does the mass on the periodic table for a particular element not equal the mass of any atom of
that element.

Mass number is always an integer. Atomic mass is never an integer number for several reasons: The atomic mass reported on a periodic table is the weighted average of all the naturally occuring isotopes. ... The mass of an atom isn't what you'd get by adding up the masses of its individual protons, neutrons and electrons.

Explanation:

a boiling water reactor does not boil the water. a pressurized water reactor boils the water faster. a pressurized water reactor is heated directly by the core. a pressurized water reactor does not use fission.